The present invention relates to improvements in methods and apparatus for recovering and pulping wastepaper, and more particularly for removing the elongate contaminants including strings, wires, bands and so forth from stock.
In arrangements heretofore available in conventional wastepaper recovery systems, elongate contaminants which cannot be allowed to remain in the pulp are removed from the pulp in a relatively high consistency stock. Such materials as strings, wires, bands and so forth which occur in bundled waste are removed at 3% to 5% consistency from the pulper by a device termed a "ragger". The long slender contaminants are twisted into a rope and continuously pulled out of the pulper. This arrangement, however, only works at a relatively low consistency, such as below approximately 6%.
For various reasons, it is advantageous to do repulping of waste at higher consistencies, such as in the 10% to 16% range which effects chemical and energy savings. Decontamination of the stock and removal of the slender contaminants has not been possible at these higher consistencies, and this has prevented high consistency pulpers from being operated continuously and particularly because of the difficulty or impossibility of the removal of long stringy contaminants from the thin stock.
It is accordingly an object of the present invention to provide an improved method and apparatus for the removal of long slender contaminants, such as wires, bands and strings, from waste stock and particularly which will operate successfully at high consistencies, that is, where the water to pulp ratio is relatively high.
A further object of the invention is to provide a simplified and improved method and apparatus for removal of long slender contaminants from wastepaper stock in a repulping operation which is capable of being operated over a range of consistencies.